Current semiconductor manufacturing capabilities meet the requirements of technology nodes of 130 to 180 nm. It is predicted that the node size will shrink to about 70 nm by the year 2006. Individual trenches and other gap type features produced in any given technology node have principal dimensions that are significantly smaller than the critical dimensions that define the current technology. Thus, it is not unusual to find gaps on the order of 100 nm or less. In future years, these feature sizes will shrink to even smaller dimensions. Current deposition processes have difficulty filling such small gaps. Unless the processes are extremely conformal, the gaps pinch off at their necks. Compounding the problem is the fact that many of these gaps have relatively high aspect ratios, on the order of at least 6:1. Examples of situations where one can find these dimensions and geometries include damascene copper line processes, shallow trench isolation, and interlayer dielectric (ILD) applications.
Filling such trenches in a reliable manner, while avoiding voids in the fill material is particularly challenging at this scale. Current processes including Physical Vapor Deposition (PVD) and Plasma Enhanced Chemical Vapor Deposition (PECVD), including High Density Plasma Chemical Vapor Deposition (HDP CVD), each of which presents some issues for filling small dimension, high aspect ratio features. Atomic Layer Deposition (ALD) and subatmospheric chemical vapor deposition (SACVD) are effective in many instances, because of the conformal nature of deposition. However, they are inappropriate for situations where the dimension of the neck is narrower than the rest of the feature. This is because the conformal nature of the deposition leads to “pinching off”, where the reentrant features are not completely filled before the entrance to the feature is sealed off. In addition, conformal deposition often leads to weak spots or seams in structures with vertical walls.
What is therefore needed is an improved deposition technique for creating void free fill in very narrow dimension features.